Micro-electro mechanical system

ABSTRACT

A micro electro-mechanical system for displacing a water based liquid is provided. The system includes an actuator having a first surface for applying a pressure to the liquid and a second surface opposite the first surface. The second surface is of a hydrophobic material. A region of the system adjacent the second surface is also of a hydrophobic material. The system has particular application in ink jet printing.

CROSS REFERENCES TO RELATED APPLICATIONS

The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, US patent applications identified by their U.S. patent application serial numbers (USSN) are listed alongside the Australian applications from which the US patent applications claim the right of priority.

CROSS-REFERENCED U.S. PAT. NO./ AUSTRALIAN PATENT APPLICATION (CLAIMING PROVISIONAL PATENT RIGHT OF PRIORITY FROM AUSTRALIAN DOCKET APPLICATION NO. PROVISIONAL APPLICATION) NO. PO7991 09/113,060 ART01 PO8505 09/113,070 ART02 PO7988 09/113,073 ART03 PO9395 09/112,748 ART04 PO8017 09/112,747 ART06 PO8014 09/112,776 ART07 PO8025 09/112,750 ART08 PO8032 09/112,746 ART09 PO7999 09/112,743 ART10 PO7998 09/112,742 ART11 PO8031 09/112,741 ART12 PO8030 09/112,740 ART13 PO7997 09/112,739 ART15 PO7979 09/113,053 ART16 PO8015 09/112,738 ART17 PO7978 09/113,067 ART18 PO7982 09/113,063 ART19 PO7989 09/113,069 ART20 PO8019 09/112,744 ART21 PO7980 09/113,058 ART22 PO8018 09/112,777 ART24 PO7938 09/113,224 ART25 PO8016 09/112,804 ART26 PO8024 09/112,805 ART27 PO7940 09/113,072 ART28 PO7939 09/112,785 ART29 PO8501 09/112,797 ART30 PO8500 09/112,796 ART31 PO7987 09/113,071 ART32 PO8022 09/112,824 ART33 PO8497 09/113,090 ART34 PO8020 09/112,823 ART38 PO8023 09/113,222 ART39 PO8504 09/112,786 ART42 PO8000 09/113,051 ART43 PO7977 09/112,782 ART44 PO7934 09/113,056 ART45 PO7990 09/113,059 ART46 PO8499 09/113,091 ART47 PO8502 09/112,753 ART48 PO7981 09/113,055 ART50 PO7986 09/113,057 ART51 PO7983 09/113,054 ART52 PO8026 09/112,752 ART53 PO8027 09/112,759 ART54 PO8028 09/112,757 ART56 PO9394 09/112,758 ART57 PO9396 09/113,107 ART58 PO9397 09/112,829 ART59 PO9398 09/112,792 ART60 PO9399 6,106,147 ART61 PO9400 09/112,790 ART62 PO9401 09/112,789 ART63 PO9402 09/112,788 ART64 PO9403 09/112,795 ART65 PO9405 09/112,749 ART66 PP0959 09/112,784 ART68 PP1397 09/112,783 ART69 PP2370 09/112,781 DOT01 PP2371 09/113,052 DOT02 PO8003 09/112,834 Fluid01 PO8005 09/113,103 Fluid02 PO9404 09/113,101 Fluid03 PO8066 09/112,751 IJ01 PO8072 09/112,787 IJ02 PO8040 09/112,802 IJ03 PO8071 09/112,803 IJ04 PO8047 09/113,097 IJ05 PO8035 09/113,099 IJ06 PO8044 09/113,084 IJ07 PO8063 09/113,066 IJ08 PO8057 09/112,778 IJ09 PO8056 09/112,779 IJ10 PO8069 09/113,077 IJ11 PO8049 09/113,061 IJ12 PO8036 09/112,818 IJ13 PO8048 09/112,816 IJ14 PO8070 09/112,772 IJ15 PO8067 09/112,819 IJ16 PO8001 09/112,815 IJ17 PO8038 09/113,096 IJ18 PO8033 09/113,068 IJ19 PO8002 09/113,095 IJ20 PO8068 09/112,808 IJ21 PO8062 09/112,809 IJ22 PO8034 09/112,780 IJ23 PO8039 09/113,083 IJ24 PO8041 09/113,121 IJ25 PO8004 09/113,122 IJ26 PO8037 09/112,793 IJ27 PO8043 09/112,794 IJ28 PO8042 09/113,128 IJ29 PO8064 09/113,127 IJ30 PO9389 09/112,756 IJ31 PO9391 09/112,755 IJ32 PP0888 09/112,754 IJ33 PP0891 09/112,811 IJ34 PP0890 09/112,812 IJ35 PP0873 09/112,813 IJ36 PP0993 09/112,814 IJ37 PP0890 09/112,764 IJ38 PP1398 09/112,765 IJ39 PP2592 09/112,767 IJ40 PP2593 09/112,768 IJ41 PP3991 09/112,807 IJ42 PP3987 09/112,806 IJ43 PP3985 09/112,820 IJ44 PP3983 09/112,821 IJ45 PO7935 09/112,822 IJM01 PO7936 09/112,825 IJM02 PO7937 09/112,826 IJM03 PO8061 09/112,827 IJM04 PO8054 09/112,828 IJM05 PO8065 6,071,750 IJM06 PO8055 09/113,108 IJM07 PO8053 09/113,109 IJM08 PO8078 09/113,123 IJM09 PO7933 09/113,114 IJM10 PO7950 09/113,115 IJM11 PO7949 09/113,129 IJM12 PO8060 09/113,124 IJM13 PO8059 09/113,125 IJM14 PO8073 09/113,126 IJM15 PO8076 09/113,119 IJM16 PO8075 09/113,120 IJM17 PO8079 09/113,221 IJM18 PO8050 09/113,116 IJM19 PO8052 09/113,118 IJM20 PO7948 09/113,117 IJM21 PO7951 09/113,113 IJM22 PO8074 09/113,130 IJM23 PO7941 09/113,110 IJM24 PO8077 09/113,112 IJM25 PO8058 09/113,087 IJM26 PO8051 09/113,074 IJM27 PO8045 6,111,754 IJM28 PO7952 09/113,088 IJM29 PO8046 09/112,771 IJM30 PO9390 09/112,769 IJM31 PO9392 09/112,770 IJM32 PP0889 09/112,798 IJM35 PP0887 09/112,801 IJM36 PP0882 09/112,800 IJM37 PP0874 09/112,799 IJM38 PP1396 09/113,098 IJM39 PP3989 09/112,833 IJM40 PP2591 09/112,832 IJM41 PP3990 09/112,831 IJM42 PP3986 09/112,830 IJM43 PP3984 09/112,836 IJM44 PP3982 09/112,835 IJM45 PP0895 09/113,102 IR01 PP0870 09/113,106 IR02 PP0869 09/113,105 IR04 PP0887 09/113,104 IR05 PP0885 09/112,810 IR06 PP0884 09/112,766 IR10 PP0886 09/113,085 IR12 PP0871 09/113,086 IR13 PP0876 09/113,094 IR14 PP0877 09/112,760 IR16 PP0878 09/112,773 IR17 PP0879 09/112,774 IR18 PP0883 09/112,775 IR19 PP0880 09/112,745 IR20 PP0881 09/113,092 IR21 PO8006 6,087,638 MEMS02 PO8007 09/113,093 MEMS03 PO8008 09/113,062 MEMS04 PO8010 6,041,600 MEMS05 PO8011 09/113,082 MEMS06 PO7947 6,067,797 MEMS07 PO7944 09/113,080 MEMS09 PO7946 6,044,646 MEMS10 PO9393 09/113,065 MEMS11 PP0875 09/113,078 MEMS12 PP0894 09/113,075 MEMS13

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to the facilitation of actuator movement in a micro-electro mechanical system (MEMs).

BACKGROUND OF THE INVENTION

Recently, micro-electro mechanical systems have become increasingly popular and rely upon the construction of small scale devices utilizing semi-conductor fabrication techniques. One form of utilization of such systems is in the displacement of a liquid for, for example, printing.

Ideally, any such system should use a low amount of energy so as to provide for an energy efficient displacement of the liquid.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved level of efficiency in a MEMS.

In accordance with the present invention there is provided a MEMS including an actuator for instigating displacement of a water-based liquid, wherein the actuator has a first surface for applying pressure to the liquid and a second surface opposite the first surface. The second surface includes a hydrophobic material. Further, the surfaces adjacent the second surface are also hydrophobic.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view of a single ink jet nozzle arrangement in its quiescent state, incorporating a preferred embodiment of the invention;

FIG. 2 is a cross-sectional schematic diagram of the ink jet nozzle arrangement of FIG. 1 in an activated state.

FIG. 3 is a schematic cross-sectional diagram of the ink jet nozzle arrangement of FIG. 1 in a deactivated state.

FIG. 4 is a schematic cross-sectional diagram of the ink jet nozzle arrangement of FIG. 1, after returning to its quiescent state.

FIG. 5 is a schematic, cross-sectional perspective diagram of a single ink jet nozzle arrangement, incorporating the preferred embodiment of the invention.

FIG. 6 is a perspective view, partly in section, of an array of the ink jet nozzle arrangements off FIG. 5.

FIG. 7 is an exploded perspective view illustrating the structure of the ink jet nozzle arrangement of FIG. 5.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

The preferred embodiment of the present invention is described with reference to an ink jet printing mechanism which is required to eject ink with a low energy consumption to ensure energy efficient operation of the printing mechanism. The present invention should not necessarily be restricted to the field of ink jet printing, as will be readily evident.

FIGS. 1 to 4, there is illustrated the basis of operation of an ink jet nozzle arrangement utilizing a thermal actuator. Turning initially to FIG. 1, there is illustrated at 1, the quiescent position of a thermal actuator 2 in a nozzle chamber 3 filled with ink and having an ink ejection port 4 for the ejection of ink. The port 4 has an ink meniscus 5 in a state of surface tension ready for the ejection of ink. The thermal actuator 2 is coated on a first surface 6, facing the chamber 3, with a hydrophilic material. A second surface 7 is coated with a hydrophobic material which causes the creation of an air bubble 8 having a meniscus 9 underneath the actuator 2. The air bubble 8 is formed over time by outgassing from the ink within the chamber 3 and the meniscus 9 is shown in an equilibrium position between the hydrophobic surface 7 and the hydrophilic surface 6. The actuator 2 is fixed at one end 11 to a substrate 12 from which it also derives an electrical connection.

When it is desired to eject a drop from the port 4, the actuator 2 is activated as shown in FIG. 2, resulting in a movement in a direction 14, the movement causing a substantial increase in the pressure of the ink around the port 4. This results in a general expansion of the meniscus 5 and the passing of momentum to the ink so as to form a partial drop 15. Upon movement of the actuator 2 in the direction 14, the ink meniscus 9 collapses generally in the indicated direction 16.

Subsequently, the thermal actuator 2 is deactivated as illustrated in FIG. 3, resulting in a return of the actuator 2 in the direction generally indicated by the arrow 17. This movement of the actuator 17 results in a low pressure region being set up in the ink within an area proximate the port 4. The, forward momentum of the drop 15 and the low pressure around the port 4 results in the ink drop 15 being broken off from the main body of the ink. The drop 15 continues to the print media as required. The movement of the actuator 2 in the direction 17 further causes ink to flow in the direction 19 around the actuator 2 in addition to causing the meniscus 9 to move as a result of the ink flow 19. Further, ink 20 is sucked into the chamber 3 to refill the ejected ink 15.

Finally, as illustrated in FIG. 4, the actuator 2 returns to its quiescent with the meniscus 5 also returning to a state of having a slight bulge. The actuator 2 is then in a suitable condition for refiring another drop on demand as required.

In one form of implementation of an inkjet printer utilizing the method illustrated in FIGS. 1 to 4, standard semi-conductive fabrication techniques are utilized in addition to standard micro-electro-mechanical techniques to construct a suitable print device having a polarity of the chambers as illustrated in FIG. 1 with corresponding actuators 2.

Turning now to FIG. 5, there is illustrated a cross-section through one form of suitable nozzle chamber. One end 11 of the actuator 2 is connected to the substrate 12 and the other end includes a stiff paddle 25 for ejecting the ink. The actuator itself is constructed from a four layer MEMs processing technique. The layers are as follows:

1. A polytetrafluoroethylene (PTFE) lower layer 26. PTFE has a very high coefficient of thermal expansion (approximately 770×10⁻⁶, or around 380 times that of silicon). This layer expands when heated by a heater layer.

2. A heater layer. A serpentine heater 27 is etched in this layer, which may be formed from nichrome, copper or any other suitable material with a resistivity such that the drive voltage for the heater 27 is compatible with the drive transistors utilized. The serpentine heater 27 is arranged to have very little tensile strength in the direction 29 along the length of the actuator.

3. A PTFE upper layer 30 on the lower VTFE layer 26. This layer 30 expands when heated by the heater layer.

4. A silicon nitride layer 32 on the upper PTFE layer 30. This is a thin layer 32 and is of high stiffness and low coefficient of thermal expansion. Its purpose is to ensure that the actuator bends, instead of simply elongating as a result of thermal expansion of the PTFE layers. Silicon nitride can be used simply because it is a standard semi-conductor material, and SiO₂ cannot easily be used if it is also the sacrificial material used when constructing the device.

Operation of the ink jet actuator 2 will then be as follows:

1. When data signals distributed to the print-head indicate that a particular nozzle arrangement is to eject a drop of ink, the drive transistor for that nozzle arrangement is turned on. This energises the heater 27 in the paddle for that nozzle arrangement. The heater is energized for approximately 2 μs, with the actual duration depending upon the design chosen for the actuator nozzle and the inks utilized.

2. The heater 27 heats the PTFE layers 26, 30 which expand at a rate many times that of the Si₃N₄ layer 32. This expansion causes the actuator 2 to bend, with the PTFE layer 26 being on a resultant convex side. The bending of the actuator moves the paddle, pushing ink out of the nozzle. The air bubble 8 (FIG. 1) between the paddle and the substrate, forms due to the hydrophobic nature of the PTFE on the back surface of the paddle. This air bubble reduces the thermal coupling to the hot side of the actuator, achieving a higher temperature with lower power. The cold side of the actuator including the SiN layer 32 is cooled by the ink. The air bubble will also expand slightly when heated, helping to move the paddle. The presence of the air bubble also means that less ink is required to move under the paddle when the actuator is energized. These three factors lead to a lower power consumption of the actuator.

3. When the heater current is turned off, as noted previously, the paddle 25 begins to return to its quiescent position. The paddle return ‘sucks’ some of the ink back into the nozzle, causing an ink ligament connecting the ink drop to the ink in the nozzle to thin. The forward velocity of the drop and the backward velocity of the ink in the chamber are resolved by the ink drop breaking off from the ink in the nozzle. The ink drop then continues towards the recording medium.

4. The actuator 2 is finally at rest in the quiescent position until the next drop ejection cycle.

Nozzle Construction

Turning now initially to FIG. 6, there is illustrated a cross section through one form of print-head 40 constructed in accordance with the preferred embodiment.

The print-head 40 has one actuator 2 associated with each of a multitude of nozzle chambers eg. 41, 42. The print-head 40 has the following major parts:

1. a drive circuitry layer 43 for driving the actuator 2.

2. A nozzle hole 4. The radius of the nozzle hole 4 is an important determinant of drop velocity and drop size.

3. An actuator 2. One end of the actuator is physically connected to the substrate and is made of four layers: a PTFE layer, a nichrome heater and stiffener layer, a second PTFE layer, and a silicon nitride layer as previously discussed.

4. The paddle 25. The paddle 25 is simply a stiff object connected to the actuator which pushes against the ink when the actuator is energized. For fabrication simplicity, the paddle can be fabricated from the same layers as the rest of the actuator 2.

5. A nozzle chamber 41. The nozzle chamber 41 is slightly wider than the actuator 2. The gap between the paddle and the nozzle chamber is determined by the fluid dynamics of the ink ejection process. The nozzle chamber 41 is also tall enough so that air ingested through the nozzle tip when the paddle returns to its quiescent state does not extend to the paddle. If it does, the ingested bubble may form a cylindrical surface instead of a hemispherical surface. If this happens, the nozzle will not refill properly. A depth of approximately 20 μm is suitable.

6. Sacrificial etch holes, e.g 47. The nozzle chamber 41 can be fabricated by a known sacrificial etch process, in which layers of a sacrificial material (eg. glass) are deposited, and subsequently etched away. The etchant used for SiO₂ is typically based on hydrofluoric acid (HF). The etching of the sacrificial layers would take too long (and therefore etch too much of the other layers) if the etchant could only enter the nozzle chambers and ink channels etc., via the nozzles eg 4. Therefore, extra holes, e.g. 47 are placed in the nozzle plate to allow the etchant to enter. These holes are made small enough that the surface tension of the ink prevents them from having any significant effect on the operations of the inkjet head.

7. A filter 50. The filter 50 is integrated as part of the device. There are no manufacturing steps which are dedicated to the fabrication of a filter. Instead, the filter 50 is a series of posts fabricated in the same process step as the nozzle chamber walls eg. 51. These posts 52 are very evenly spaced, to form an absolute filter with a filter ‘pore’ size equal to the spacing between the posts.

8. Ink channels 55. These channels 55 are fabricated in the same manner as the nozzle chambers 3. They connect an ink inlet 56 to a series of nozzle chambers.

9. Ink inlets 56. Ink inlet holes are etched from the back of a print-head wafer to the ink channels running along the front of the print-head. Ink is provided to the back surfaced of the wafer, and fills the nozzle chambers by capillarity action.

10. The air bubble 8. The underside of the paddle is PTFE, a highly hydrophobic material. As the ink is only at atmospheric pressure, surface tension prevents the region under the paddle from filling with ink. The presence of an air bubble under the paddle increases the efficiency of the device, as there is less requirement for ink flow around the bottom of the paddle upon movement of the actuator 2. Also, the air bubble is on the side of the actuator 2 which must become hot when energized, while the cold side of the actuator is in contact with water. This leads to a significant improvement in thermal efficiency, and lower energy operation. An alternative system which fills completely and does not have an air bubble under the paddle can easily be constructed by depositing a thin hydrophilic layer (such as Si₂N₄) before the PTFE is deposited.

A significant advantage of the arrangement of FIG. 6 is the nozzle chambers, e.g. 41, 42, are themselves compact and further compactly arranged around the ink channel 55. For example, a page with photographic print-head may be 10 cm in length while an A4 print-head may be 20 cm in length. Scanning print-heads, on the other hand may be nearly 1 cm long. An advantage of the arrangement in FIG. 6 is that the width of any print-head is extremely small. Such a small width allows a large number of print-heads to be constructed on the one silicon wafer, thereby increasing the yields as a result of the small overall area of each print-head.

Basic Fabrications Sequence

One form of print-head fabrication sequence utilizing MEMs technology will now be described. The description assumes that the reader is familiar with surface and micro-machining techniques utilized for the construction of MEMs devices, including the latest proceedings in these areas. Turning now to FIG. 7, there is illustrated an exploded perspective view of a single ink jet nozzle as constructed in accordance with the preferred embodiment. The construction of a print-head can proceed as follows:

1. Start with a standard single crystal silicon wafer 80 suitable for the desired manufacturing process of the active semiconductor device technology chosen. Here the manufacturing process is assumed to be 0.5μ CMOS.

2. Complete fabrication the CMOS circuitry layer 83, including an oxide layer (not shown) and passivation layer 82 for passivation of the wafer. As the chip will be immersed in water bad ink, the passivation layer must be highly impervious. A layer of high density silicon nitride (Si₃N₄) is suitable. Another alternative is diamond-like carbon (DLC).

3. Deposit 2μ of phosphosilicate glass (PSG). This will be a sacrificial layer which raises the actuator and paddle from the substrate. This thickness is not critical.

4. Etch the PSG to leave islands under the actuator positions on which the actuators will be formed.

5. Deposit 1.0 μm of polytetrafluoroethylene (PTFE) layer 84. The PTFE may be roughened to promote adhesion. The PTFE may be deposited as a spin-on nano-emulsion. [T. Rosenmayer, H. Wu, “PTFE nano-emulsions as spinon, low dielectric constant materials for ULSI applications”, PP463-468, Advanced Metallisation for Future ULSI, MRS vol. 427,1996].

6. Mask and etch via holes through to the top level metal of the CMOS circuitry for connection of a power supply to the actuator (not shown). Suitable etching procedures for PTFE are discussed in “Thermally assisted Ian Beam Etching of polytetrafluoroethylene: A new technique for High Aspect Ratio Etching of MEMS” by Berenschot et al in the Proceedings of the Ninth Annual International Workshop on Micro Electro Mechanical Systems, San Diego, February 1996.

7. Deposit the heater material layer 85. This may be Nichrome (an alloy of 80% nickel and 20% chromium) which may be deposited by sputtering. Many other heater materials may be used. The principal requirements are a resistivity which results in a drive voltage which is suitable for the CMOS drive circuitry layer, a melting point above the temperature of subsequent process steps, electro-migration resistance, and appropriate mechanical properties.

8. Etch the heater material using a mask pattern of the heater and the paddle stiffener.

9. Deposit 2.0 μm of PTFE. As with step 5, the PTFE may be spun on as a nano-emulsion, and may be roughened to promote adhesion. (This layer forms part of layer 84 in FIG. 7.)

10. Deposit via a mask 0.25 of silicon nitride for the top of the layer 86 of the actuator, or any of a wide variety of other materials having suitable properties as previously described. The major materials requirements are: a low coefficient of thermal expansion compared to PTFE; a relatively high Young's modulus, does not corrode in water, and a low etch rate in hydrofluoric acid (HF). The last of these requirements is due to the subsequent use of HF to etch the sacrificial glass layers. If a different sacrificial layer is chosen, then this layer should obviously have resistance to the process used to remove the sacrificial material.

11. Using the silicon nitride as a mask, etch the PTFE, PTFE can be etched with very high selectivity (>1,000 to one) with ion beam etching. The wafer may be tilted slightly and rotated during etching to prevent the formation of microglass. Both layers of PTFE can be etched simultaneously.

12. Deposit 20 μm of SiO₂. This may be deposited as spin-on glass (SOG) and will be used as a sacrificial layer (not shown).

13. Etch through the glass layer using a mask defining the nozzle chamber and ink channel walls, e.g. 51, and filter posts, e.g. 52. This etch is through around 20 μm of glass, so should be highly anisotropic to minimize the chip area required. The Minimum line width is around 6 μm, so coarse lithography may be used. Overlay alignment error should preferably be less than 0.5 μm. The etched areas are subsequently filled by depositing silicon nitride through the mask.

14. Deposit 2 μm of silicon nitride layer 87. This forms the front surface of the print-head. Many other materials could be used. A suitable material should have a relatively high Young's modulus, not corrode in water, and have a low etch rate in hydrofluoric acid (HF). It should also be hydrophilic.

15. Mask and etch nozzle rims (not shown). These are 1 μm annular protrusions above the print-head surface around the nozzles, e.g. 4, which help to prevent ink flooding the surface of the print-head. They work in conjunction with the hydrophobic front surface of the print-head.

16. Mask and etch the nozzle holes 4. This mask also includes smaller holes, e.g. 47, which are placed to allow the ingress of the etchant for the sacrificial layers. These holes should be small enough to that the ink surface tension ensures that ink is not ejected from the holes when the ink pressure waves from nearby actuated nozzles is at a maximum. Also, the holes should be small enough to ensure that air bubbles are not ingested at times of low ink pressure. These holes are spaced close enough so that etchant can easily remove all of the sacrificial material even though the paddle and actuator are fairly large and flexible, stiction should not be a problem for this design. This is because the paddle is made from PTFE.

17. Etch ink access holes 56 (FIG. 6) through the wafer 80. This can be done as an anisotropic crystallographic silicon etch, or an anisotropic dry etch. A dry etch system capable of high aspect ratio deep silicon trench etching such as the Surface Technology Systems (STS) Advance Silicon Etch (ASE) system is recommended for volume production, as the chip size can be reduced over wet etch. The wet etch is suitable for small volume production, as the chip size can be reduced over wet etch. The wet etch is suitable for small volume production where a suitable plasma etch system is not available. Alternatively, but undesirably, ink access can be around the sides of the print-head chips. If ink access is through the wafer higher ink flow is possible, and there is less requirement for high accuracy assembly. If ink access is around the edge of the chip, ink flow is severely limited, and the print-head chips must be carefully assembled onto ink channel chips. This latter process is difficult due to the possibility of damaging the fragile nozzle plate. If plasma etching is used, the chips can be effectively diced at the same time. Separating the chips by plasma etching allows them to be spaced as little as 35 μm apart, increasing the number of chips on a wafer. At this stage, the chips must be handled carefully, as each chip is a beam of silicon 100 mm long by 0.5 mm wide and 0.7 mm thick.

18. Mount the print-head chips into print-head carriers. These are mechanical support and ink connection mouldings. The print-head carriers can be moulded from plastic, as the minimum dimensions are 0.5 mm.

19. Probe test the print-heads and bond the good print-heads. Bonding may be by wire bonding or TAB bonding.

20. Etch the sacrificial layers. This can be done with an isotropic wet etch, such as buffered HF. This stage is performed after the mounting of the print-heads into moulded print-head carriers, and after bonding, as the front surface of the print-heads is very fragile after the sacrificial etch has been completed. There should be no direct handling of the print-head chips after the sacrificial etch.

21. Hydrophobize the front surface of the printheads.

22. Fill with ink and perform final testing on the completed printheads.

It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiment without departing from the spirit or scope of the invention as broadly described. The present embodiment is, therefore, to be considered in all respects to be illustrative and not restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per print head, but is a major impediment to the fabrication of pagewidth printheads with 19,200 nozzles.

Ideally, the ink jet technologies used meet the stringent requirement of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table under the heading Cross References to Related Applications.

The ink jet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems.

For ease of manufacture using standard process equipment, the printhead is designed to be a monolithic 0.5 micron CMOS chip with MEMS post processing. For color photographic applications, the printhead is 100 mm long, with a width which depends upon the ink jet type. The smallest printhead designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The printheads each contain 19,200 nozzles plus data and control circuitry.

Ink is supplied to the back of the printhead by injection molded plastic ink channels. The molding requires 50 micron features, which can be created using a lithographically micromachined insert in a standard injection molding tool. Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The printhead is connected to the camera circuitry by tape automated bonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of ink jet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJ01 to IJ45 above which match the docket numbers in the table under the heading Cross References to Related Applications.

Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet printheads with characteristics superior to any currently available ink jet technology.

Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, a print technology may be listed more than once in a table, where it shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrix are set out in the following tables.

ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS) Description Advantages Disadvantages Examples Thermal bubble An electrothermal heater heats Large force generated High power Canon Bubblejet 1979 Endo et the ink to above boiling point, Simple construction Ink carrier limited to water al GB patent 2,007,162 transferring significant heat to No moving parts Low efficiency Xerox heater-in-pit 1990 the aqueous ink. A bubble Fast operation High temperatures required Hawkins et al U.S. Pat. No. nucleates and quickly forms, Small chip area required for High mechanical stress 4,899,181 expelling the ink. The efficiency actuator Unusual materials required Hewlett-Packard TIJ 1982 of the process is low, with Large drive transistors Vaught et al U.S. Pat. No. typically less than 0.05% of the Cavitation causes actuator 4,490,728 electrical energy being trans- failure formed into kinetic energy of the Kogation reduces bubble drop. formation Large print heads are difficult to fabricate Piezoelectric A piezoelectric crystal such as Low power consumption Very large area required for Kyser et al U.S. Pat. No. lead lanthanum zirconate (PZT) Many ink types can be used actuator 3,946,398 is electrically activated, and Fast operation Difficult to integrate with Zoltan U.S. Pat. No. 3,683,212 either expands, shears, or bends High efficiency electronics 1973 Stemme U.S. Pat. No. to apply pressure to the ink, High voltage drive transistors 3,747,120 ejecting drops. required Epson Stylus Full pagewidth print heads Tektronix impractical due to actuator IJ04 size Requires electrical poling in high field strengths during manufacture Electrostrictive An electric field is used to Low power consumption Low maximum strain (approx. Seiko Epson, Usui et all JP activate electrostriction in Many ink types can be used 0.01%) 253401/96 relaxor materials such as lead Low thermal expansion Large area required for actuator IJ04 lanthanum zirconate titanate Electric field strength required due to low strain (PLZT) or lead magnesium (approx. 3.5 V/μm) can be Response speed is marginal niobate (PMN). generated without difficulty (˜10 μs) Does not require electrical High voltage drive transistors poling required Full pagewidth print heads impractical due to actuator size Ferroelectric An electric field is used to Low power consumption Difficult to integrate with IJ04 induce a phase transition Many ink types can be used electronics between the antiferroelectric Fast operation (<1 μs) Unusual materials such as (AFE) and ferroelectric (FE) Relatively high longitudinal PLZSnT are required phase. Perovskite materials such strain Actuators require a large area as tin modified lead lanthanum High efficiency zirconate titanate (PLZSnT) Electric field strength of exhibit large strains of up to 1% around 3 V/μm can be readily associated with the AFE to FE provided phase transition. Electrostatic Conductive plates are separated Low power consumption Difficult to operate electro- IJ02, IJ04 plates by a compressible or fluid Many ink types can be used static devices in an aqueous dielectric (usually air). Upon Fast operation environment application of a voltage, the The electrostatic actuator will plates attract each other and normally need to be separated displace ink, causing drop from the ink ejection. The conductive plates Very large area required to may be in a comb or honeycomb achieve high forces structure, or stacked to increase High voltage drive transistors the surface area and therefore may be required the force. Full pagewidth print heads are not competitive due to actuator size Electrostatic A strong electric field is applied Low current consumption High voltage required 1989 Saito et al, U.S. Pat. No. pull on ink to the ink, whereupon electro- Low temperature May be damaged by sparks due 4,799,068 static attraction accelerates the to air breakdown 1989 Miura et al, U.S. Pat. No. ink towards the print medium. Required field strength increases 4,810,954 as the drop size decreases Tone-jet High voltage drive transistors required Electrostatic field attracts dust Permanent An electromagnet directly Low power consumption Complex fabrication IJ07, IJ10 magnet electro- attracts a permanent magnet, Many ink types can be used Permanent magnetic material magnetic displacing ink and causing drop Fast operation such as Neodymium Iron Boron ejection. Rare earth magnets High efficiency (NdFeB) required. with a field strength around Easy extension from single High local currents required 1 Tesla can be used. Examples nozzles to pagewidth print Copper metalization should be are: Samarium Colbalt (SaCo) heads used for long electromigration and magnetic materials in the lifetime and low resistivity neodymium iron boron family Pigmented inks are usually (NdFeB, NdDyFeBNb, infeasible NdDyFeB, etc) Operating temperature limited to the Curie (around 540 K.) Soft magnetic A solenoid induced a magnetic Low power consumption Complex fabrication IJ01, IJ05, IJ08, IJ10, IJ12, core electro- field in a soft magnetic core or Many ink types can be used Materials not usually present in IJ14, IJ15, IJ17 magnetic yoke fabricated from a ferrous Fast operation a CMOS fab such as NiFe, material such as electroplated High efficiency CoNiFe, or CoFe are required iron alloys such as CoNiFe [1], Easy extension from single High local currents required CoFe, or NiFe alloys. Typically, nozzles to pagewidth print Copper metalization should be the soft magnetic material is in heads used for long electromigration two parts, which are normally lifetime and low resistivity held apart by a spring. When the Electroplating is required solenoid is actuated, the two High saturation flux density is parts attract, displacing the ink. required (2.0-2.1 T is achievable with CoNiFe [1]) Lorenz force The Lorenz force acting on a Low power consumption Force acts as a twisting motion IJ06, IJ11, IJ13, IJ16 current carrying wire in a Many ink types can be used Typically, only a quarter of the magnetic field is utilized. This Fast operation solenoid length provides force in allows the magnetic field to be High efficiency a useful direction supplied externally to the print Easy extension from single High local currents required head, for example with rare nozzles to pagewidth print Copper metalization should be earth permanent magnets. Only heads used for long electromigration the current carrying wire need be lifetime and low resistivity fabricated on the printhead, Pigmented inks are usually simplifying materials require- infeasible ments. Magneto- The actuator uses the giant Many ink types can be used Force acts as a twisting motion Fischenbeck, U.S. Pat. No. striction magnetostrictive effect of Fast operation Unusual materials such as 4,032,929 materials such as Terfenol-D (an High efficiency Terfenol-D are required IJ25 alloy of terbium, dysprosium Easy extension from single High local currents required and iron developed at the Naval nozzles to pagewidth print Copper metalization should be Ordnance Laboratory, hence heads used for long electromigration Ter-Fe-NOL). For best High force is available lifetime and low resistivity efficiency, the actuator should Pre-stressing may be required be pre-stressed to approx. 8 MPa. Surface tension Ink under positive pressure is Low power consumption Requires supplementary force to Silverbrook, EP 0771 658 A2 reduction held in a nozzle by surface Simple construction effect drop separation and related patent applications tension. The surface tension of No unusual materials required in Requires special ink surfactants the ink is reduced below the fabrication Speed may be limited by bubble threshold, causing the High efficiency surfactant properties ink to egress from the nozzle. Easy extension from single nozzles to pagewidth print heads Viscosity The ink viscosity is locally Simple construction Requires supplementary force to Silverbrook, EP 0771 658 A2 reduction reduced to select which drops No unusual materials required in effect drop separation and related patent applications are to be ejected. A viscosity fabrication Requires special ink viscosity reduction can be achieved Easy extension from single properties electrothermally with most inks, nozzles to pagewidth print High speed is difficult to achieve but special inks can be heads Requires oscillating ink pressure engineered for a 100:1 viscosity A high temperature difference reduction. (typically 80 degrees) is required Acoustic An acoustic wave is generated Can operate without a nozzle Complex drive curcuitry 1993 Hadimioglu et al, EUP and focussed upon the drop plate Complex fabrication 550,192 ejection region. Low efficiency 1993 Elrod et al, EUP 572,220 Poor control of drop position Poor control of drop volume Thermoelastic An actuator which relies upon Low power consumption Efficient aqueous operation IJ03, IJ09, IJ17, IJ18, IJ19, IJ20, bend actuator differential thermal expansion Many ink types can be used requires a thermal insulator on IJ21, IJ22, IJ23, IJ24, IJ27, IJ28, upon Joule heating is used. Simple planar fabrication the hot side IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, Small chip area required for Corrosion prevention can be IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, each actuator difficult IJ41 Fast operation Pigmented inks may be High efficiency infeasible, as pigment particles CMOS compatible voltages and may jam the bend actuator currents Standard MEMS processes can be used Easy extension from single nozzles to pagewidth print heads High CTE A material with a very high High force can be generated Requires special material (e.g. IJ09, IJ17, IJ18, IJ20, IJ21, IJ22, thermoelastic coefficient of thermal expansion Three methods of PTFE PTFE) IJ23, IJ24, IJ27, IJ28, IJ29, IJ30, actuator (CTE) such as polytetrafluoro- deposition are under develop- Requires a PTFE deposition IJ31, IJ42, IJ43, IJ44 ethylene (PTFE) is used. As ment: chemical vapor deposition process, which is not yet high CTE materials are usually (CVD), spin coating, and standard in ULSI fabs non-conductive, a heater evaporation PTFE deposition cannot be fabricated from a conductive PTFE is a candidate for low followed with high temperature material is incorporated. A 50 dielectric constant insulation in (above 350° C.) processing μm long PTFE bend actuator ULSI Pigmented inks may be with polysilicon heater and Very low power consumption infeasible, as pigment particles 15 mW power input can provide Many ink types can be used may jam the bend actuator 180 μN force and 10 μm Simple planar fabrication deflection. Actuator motions Small chip area required for include: each actuator Bend Fast operation Push High efficiency Buckle CMOS compatible voltages and Rotate currents Easy extension from single nozzles to pagewidth print heads Conductive A polymer with a high High force can be generated Requires special materials IJ24 polymer coefficient of thermal expansion Very low power consumption development (High CTE thermoelastic (such as PTFE) is doped with Many ink types can be used conductive polymer) actuator conducting substances to Simple planar fabrication Requires a PTFE deposition increase its conductivity to about Small chip area required for process, which is not yet 3 orders of magnitude below that each actuator standard in ULSI fabs of copper. The conducting poly- Fast operation PTFE deposition cannot be mer expands when resistively High efficiency followed with high temperature heated. Examples of conducting CMOS compatible voltages and (above 350° C.) processing dopants include: currents Evaporation and CVD Carbon nanotubes Easy extension from single deposition techniques cannot be Metal fibers nozzles to pagewidth print used Conductive polymers such as heads Pigmented inks may be doped polythiophene infeasible, as pigment particles Carbon granules may jam the bend actuator Shape memory A shape memory alloy such as High force is available (stresses Fatigue limits maximum number IJ26 alloy TiNi (also known as Nitinol - of hundreds of MPa) of cycles Nickel Titanium alloy developed Large strain is available (more Low strain (1%) is required to at the Naval Ordanance than 3%) extend fatigue resistance Laboratory) is thermally High corrosion resistance Cycle rate limited by heat switched between its weak Simple construction removal martensitic state and its high Easy extension from single Requires unusual materials stiffness austenic state. The nozzles to pagewidth print (TiNi) shape of the actuator in its heads The latent heat of transformation martensitic state is deformed Low voltage operation must be provided relative to the austenic shape. High current operation The shape change causes Requires pre-stressing to distort ejection of a drop. the martensitic state Linear Linear magnetic actuators Linear Magnetic actuators can Requires unusual semiconductor IJ12 Magnetic include the Linear Induction be constructed with high thrust, materials such as soft magnetic Actuator Actuator (LIA), Linear long travel, and high efficiency alloys (e.g. CoNiFe) Permanent Magnet Synchronous using planar semiconductor Some varieties also require Actuator (LPMSA), Linear fabrication techniques permanent magnetic materials Reluctance Synchronous Long actuator travel is available such as Neodymium iron boron Actuator (LRSA), Linear Medium force is available (NdFeB) Switched Reluctance Actuator Low voltage operation Requires complex multi-phase (LSRA), and the Linear Stepper drive circuitry Actuator (LSA). High current operation

BASIC OPERATION MODE Description Advantages Disadvantages Examples Actuator This is the simplest mode of Simple operation Drop repetition rate is usually Thermal ink jet directly pushes operation: the actuator directly No external fields required limited to around 10 kHz. Piezoelectric ink jet ink supplies sufficient kinetic energy Satellite drops can be avoided if However, this is not IJ01, IJ02, IJ03, IJ04, IJ05, IJ06, to expel the drop. The drop must drop velocity is less than 4 m/s fundamental to the method, but IJ07, IJ09, IJ11, IJ12, IJ14, IJl6, have a sufficient velocity to Can be efficient, depending is related to the refill IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, overcome the surface tension. upon the actuator used method normally used IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, All of the drop kinetic energy IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, must be provided by the actuator IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Satellite drops usually form if drop velocity is greater than 4.5 m/s Proximity The drops to be printed are Very simple print head fabrica- Requires close proximity Silverbrook, EP 0771 658 A2 selected by some manner (e.g. tion can be used between the print head and the and related patent applications thermally induced surface The drop selection means does print media or transfer roller tension reduction of pressurized not need to provide the energy May require two print heads ink). Selected drops are required to separate the drop printing alternate rows of the separated from the ink in the from the nozzle image nozzle by contact with the print Monolithic color print heads are medium or a transfer roller. difficult Electrostatic The drops to be printed are Very simple print head fabrica- Requires very high electro- Silverbrook, EP 0771 658 A2 pull on ink selected by some manner (e.g. tion can be used static field and related patent applications thermally induced surface The drop selection means does Electrostatic field for small Tone-Jet tension reduction of pressurized not need to provide the energy nozzle sizes is above air ink). Selected drops are required to separate the drop breakdown separated from the ink in the from the nozzle Electrostatic field may attract nozzle by a strong electric dust field. Magnetic pull The drops to be printed are Very simple print head fabrica- Requires magnetic ink Silverbrook, EP 0771 658 A2 on ink selected by some manner (e.g. tion can be used Ink colors other than black are and related patent applications thermally induced surface The drop selection means does difficult tension reduction of pressurized not need to provide the energy Requires very high magnetic ink). Selected drops are required to separate the drop fields separated from the ink in the from the nozzle nozzle by a strong magnetic field acting on the magnetic ink. Shutter The actuator moves a shutter to High speed (>50 kHz) operation Moving parts are required IJ13, IJ17, IJ21 block ink flow to the nozzle. can be achieved due to reduced Requires ink pressure modulator The ink pressure is pulsed at a refill time Friction and wear must be multiple of the drop ejection Drop timing can be very considered frequency. accurate Stiction is possible The actuator energy can be very low Shuttered grill The actuator moves a shutter to Actuators with small travel can Moving parts are required IJ08, IJ15, IJ18, IJ19 block ink flow through a grill to be used Requires ink pressure modulator the nozzle. The shutter move- Actuators with small force can Friction and wear must be ment need only be equal to the be used considered width of the grill holes. High speed (>50 kHz) operation Stiction is possible can be achieved Pulsed A pulsed magnetic field attracts Extremely low energy operation Requires an external pulsed IJ10 magnetic pull an ‘ink pusher’ at the drop is possible magnetic field on ink pusher ejection frequency. An actuator No heat dissipation problems Requires special materials for controls a catch, which prevents both the actuator and the ink the ink pusher from moving pusher when a drop is not to be ejected. Complex construction

AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) Description Advantages Disadvantages Examples None The actuator directly fires the Simplicity of construction Drop ejection energy must be Most ink jets, including piezo- ink drop, and there is no external Simplicity of operation supplied by individual nozzle electric and thermal bubble. field or other mechanism Small physical size actuator IJ01, IJ02, IJ03, IJ04, IJ05, IJ07, required. IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating The ink pressure oscillates, Oscillating ink pressure can Requires external ink pressure Silverbrook, EP 0771 658 A2 ink pressure providing much of the drop provide a refill pulse, allowing oscillator and related patent applications (including ejection energy. The actuator higher operating speed Ink pressure phase and IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, acoustic selects which drops are to be The actuators may operate with amplitude must be carefully IJ21 stimulation) fired by selectively blocking or much lower energy controlled enabling nozzles. The ink Acoustic lenses can be used to Acoustic reflections in the ink pressure oscillation may be focus the sound on the nozzles chamber must be deisgned for achieved by vibrating the print head, or preferably by an actuator in the ink supply. Media The print head is placed in close Low power Precision assembly required Silverbrook, EP 0771 658 A2 proximity proximity to the print medium. High accuracy Paper fibers may cause problems and related patent applications Selected drops protrude from the Simple print head construction Cannot print on rough substrates print head further than unselected drops, and contact the print medium. The drop soaks into the medium fast enough to cause drop separation. Transfer roll Drops are printed to a transfer High accuracy Bulky Silverbrook, EP 0771 658 A2 roller instead of straight to the Wide range of print substrates Expensive and related patent applications print medium. A transfer roller can be used Complex construction Tektronix hot melt piezoelectric can also be used for proximity Ink can be dried on the transfer ink jet drop separation. roller Any of the IJ series Electrostatic An electric field is used to Low power Field strength required for Silverbrook, EP 0771 658 A2 accelerate selected drops Simple print head construction separation of small drops is near and related patent applications towards the print medium. or above air breakdown Tone-Jet Direct A magnetic field is used to Low power Requires magnetic ink Silverbrook, EP 0771 658 A2 magnetic field accelerate selected drops of Simple print head construction Requires strong magnetic field and related patent applications magnetic ink towards the print medium. Cross magnetic The print head is placed in a Does not require magnetic Requires external magnet IJ06, IJ16 field constant magnetic field. The materials to be integrated in Current densities may be high, Lorenz force in a current the print head manufacturing resulting in electromigration carrying wire is used to move process problems the actuator. Pulsed A pulsed magnetic field is used Very low power operation is Complex print head construction IJ10 magnetic field to cyclically attract a paddle, possible Magnetic materials required in which pushes on the ink. A Small print head size print head small actuator moves a catch, which selectively prevents the paddle from moving.

ACTUATOR AMPLIFICATION OR MODIFICATION METHOD Description Advantages Disadvantages Examples None No actuator mechanical Operational simplicity Many actuator mechanisms have Thermal Bubble Ink jet amplification is used. The insufficient travel, or insufficient IJ01, IJ02, IJ06, IJ07, IJ16, IJ25, actuator directly drives the force, to effectively drive the IJ26 drop ejection process. drop ejection process Differential An actuator material expands Provides greater travel in a High stresses are involved Piezoelectric expansion more on one side than on the reduced print head area Care must be taken that the IJ03, IJ09, IJ17, IJ18, IJ19, IJ20, bend actuator other. The expansion may be materials do not delaminate IJ21, IJ22, IJ23, IJ24, IJ27, IJ29, thermal, piezoelectric, Residual bend resulting from IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, magnetostrictive, or other high temperature or high stress IJ36, IJ37, IJ38, IJ39, IJ42, IJ43, mechanism. The bend actuator during formation IJ44 converts a high force low travel actuator mechanism to high travel, lower force mechanism. Transient bend A trilayer bend actuator where Very good temperature stability High stresses are involved IJ40, IJ41 actuator the two outside layers are High speed, as a new drop can Care must be taken that the identical. This cancels bend due be fired before heat dissipates materials do not delaminate to ambient temperature and Cancels residual stress of residual stress. The actuator formation only responds to transient heat- ing of one side or the other. Reverse spring The actuator loads a spring. Better coupling to the ink Fabrication complexity IJ05, IJ11 When the actuator is turned off, High stress in the spring the spring releases. This can reverse the force/distance curve of the actuator to make it compatible with the force/time requirements of the drop ejection. Actuator stack A series of thin actuators are Increased travel Increased fabrication complexity Some piezoelectric ink jets stacked. This can be appropriate Reduced drive voltage Increased possibility of short IJ04 where actuators require high circuits due to pinholes electric field strength, such as electrostatic and piezo- electric actuators. Multiple Multiple smaller actuators are Increases the force available Actuator forces may not add IJ12, IJ13, IJ18, IJ20, IJ22, IJ28, actuators used simultaneously to move the from an actuator linearly, reduced efficiency IJ42, IJ43 ink. Each actuator need provide Multiple actuators can be only a portion of the force positioned to control ink flow required. accurately Linear Spring A linear spring is used to Matches low travel actuator with Requires print head area for the IJ15 transform a motion with small higher travel requirements spring travel and high force into a Non-contact method of motion longer travel, lower force transformation motion. Coiled actuator A bend actuator is coiled to Increases travel Generally restricted to planar IJ17, IJ21, IJ34, IJ35 provide greater travel in a Reduces chip area implementations due to extreme reduced chip area. Planar implementations are fabrication difficulty in other relatively easy to fabricate. orientations. Flexure bend A bend actuator has a small Simple means of increasing Care must be taken not to IJ10, IJ19, IJ33 actuator region near the fixture point, travel of a bend actuator exceed the elastic limit in the which flexes much more readily flexure area than the remainder of the Stress distribution is very actuator. The actuator flexing uneven is effectively converted from Difficult to accurately model an even coiling to an angular with finite element analysis bend, resulting in greater travel of the actuator tip. Catch The actuator controls a small Very low actuator energy Complex construction IJ10 catch. The catch either enables Very small actuator size Requires external force or disables movement of an ink Unsuitable for pigmented inks pusher that is controlled in a bulk manner. Gears Gears can be used to increase Low force, low travel actuators Moving parts are required IJ13 travel at the expense of duration. can be used Several actuator cycles are Circular gears, rack and pinion, Can be fabricated using standard required ratchets, and other gearing surface MEMS processes More complex drive electronics methods can be used. Complex construction Friction, friction, and wear are possible Buckle plate A buckle plate can be used to Very fast movement achievable Must stay within elastic limits of S. Hirata et al, “An Ink-jet Head change a slow actuator into a the materials for long device life Using Diaphragm Micro- fast motion. It can also convert High stresses involved actuator,” Proc. IEEE MEMS, a high force, low travel Generally high power require- Feb. 1996, pp 418-423. actuator into a high travel, ments IJ18, IJ27 medium force motion. Tapered A tapered magnetic pole can Linearizes the magnetic force/ Complex construction IJ14 magnetic pole increase travel at the expense distance curve of force. Lever A lever and fulcrum is used to Matches low travel actuator with High stress around the fulcrum IJ32, IJ36, IJ37 transform a motion with small higher travel requirements travel and high force into a Fulcrum area has no linear motion with longer travel and movement, and can be used for a lower force. The lever can also fluid seal reverse the direction of travel. Rotary impeller The actuator is connected to a High mechanical advantage Complex construction IJ28 rotary impeller. A small angular The ratio of force to travel of Unsuitable for pigmented inks deflection of the actuator results the actuator can be matched to in a rotation of the impeller the nozzle requirements by vanes, which push the ink varying the number of impeller against stationary vanes and vanes out of the nozzle. Acoustic lens A refractive or diffractive (e.g. No moving parts Large area required 1993 Hadimioglu et al, EUP zone plate) acoustic lens is used Only relevant for acoustic ink 550,192 to concentrate sound waves. jets 1993 Elrod et al, EUP 572,220 Sharp A sharp point is used to Simple construction Difficult to fabricate using Tone-jet conductive concentrate an electrostatic standard VLSI processes for a point field. surface ejecting ink-jet Only relevant for electrostatic ink jets

ACTUATOR MOTION Description Advantages Disadvantages Examples Volume The volume of the actuator Simple construction in the High energy is typically required Hewlett-Packard Thermal Ink jet expansion changes, pushing the ink in all case of thermal ink jet to achieve volume expansion. Cannon Bubblejet directions. This leads to thermal stress, cavitation, and kogation in thermal ink jet implementations Linear, normal The actuator moves in a Efficient coupling to ink drops High fabrication complexity may IJ01, IJ02, IJ04, IJ07, IJ11, IJ14 to chip surface direction normal to the print ejected normal to the surface be required to achieve head surface. The nozzle is perpendicular motion typically in the line of movement. Parallel to chip The actuator moves parallel to Suitable for planar fabrication Fabrication complexity IJ12, IJ13, IJ15, IJ33, IJ34, IJ35, surface the print head surface. Drop Friction IJ36 ejection may still be normal to Stiction the surface. Membrane An actuator with a high force The effective area of the actuator Fabrication complexity 1982 Howkins U.S. Pat. No. push but small area is used to push a becomes the membrane area Actuator size 4,459,601 stiff membrane that is in contact Difficulty of integration in a with the ink. VLSI process Rotary The actuator causes the rotation Rotary levers may be used to Device complexity IJ05, IJ08, IJ13, IJ28 of some element, such a grill or increase travel May have friction at a pivot impeller Small chip area requirements point Bend The actuator bends when A very small change in Requires the actuator to be made 1970 Kyser et al U.S. Pat. No. energized. This may be due to dimensions can be converted to from at least two distinct layers, 3,946,398 differential thermal expansion. a large motion. or to have a thermal difference 1973 Stemme U.S. Pat. No. across the actuator 3,747,120 IJ03, IJ09, IJ10, IJ19, IJ23, IJ24, IJ25, IJ29, IJ30, Ij31, IJ33, IJ34, IJ35 Swivel The actuator swivels around a Allows operation where the net Inefficient coupling to the ink IJ06 central pivot. This motion is linear force on the paddle is zero motion suitable where there are opposite Small chip area requirements forces applied to opposite sides of the paddle, e.g. Lorenz force. Straighten The actuator is normally bent, Can be used with shape memory Requires careful balance of IJ26, IJ32 and straightens when energized. alloys where the austenic phase stresses to ensure that the is planar quiescent bend is accurate Double bend The actuator bends in one One actuator can be used to Difficult to make the drops IJ36, IJ37, IJ38 direction when one element is power two nozzles. ejected by both bend directions energized, and bends the other Reduced chip size. identical. way when another element is Not sensitive to ambient A small efficiency loss energized. temperature compared to equivalent single bend actuators. Shear Energizing the actuator causes a Can increase the effective travel Not readily applicable to other 1985 Fishbeck U.S. Pat. No. shear motion in the actuator of piezoelectric actuators actuator mechanisms 4,584,590 material. Radial The actuator squeezes an ink Relatively easy to fabricate High force required 1970 Zoltan U.S. Pat. No. constriction reservoir, forcing ink from a single nozzles from glass tubing Inefficient 3,683,212 constricted nozzle. as macroscopic structures Difficult to integrate with VLSI processes Coil/uncoil A coiled actuator uncoils or coils Easy to fabricate as a planar Difficult to fabricate for non- IJ17, IJ21, IJ34, IJ35 more tightly. The motion of the VLSI process planar devices free end of the actuator ejects Small area required, therefore Poor out-of-plane stiffness the ink. low cost Bow The actuator bows (or buckles in Can increase the speed of travel Maximum travel is constrained IJ16, IJ18, IJ27 the middle when energized. Mechanically rigid High force required Push-Pull Two actuators control a shutter. The structure is pinned at both Not readily suitable for ink jets IJ18 One actuator pulls the shutter, ends, so has a high out-of-plane which directly push the ink and the other pushes it. rigidity Curl inwards A set of actuators curl inwards Good fluid flow to the region Design complexity IJ20, IJ42 to reduce the volume of ink that behind the actuator increases they enclose. efficiency Curl outwards A set of actuators curl outwards, Relatively simple construction Relatively large chip area IJ43 pressurizing ink in a chamber surrounding the actuators, and expelling ink from a nozzle in the chamber. Iris Multiple vanes enclose a volume High efficiency High fabrication complexity IJ22 of ink. These simultaneously Small chip area Not suitable for pigmented inks rotate, reducing the volume between the vanes. Acoustic The actuator vibrates at a high The actuator can be physically Large area required for efficient 1993 Hadimioglu et al, EUP vibration frequency. distant from the ink operation at useful frequencies 550,192 Acoustic coupling and crosstalk 1993 Elrod et al, EUP 572,220 Complex dirve circuitry Poor control of drop volume and position None In various ink jet designs the No moving parts Various other tradeoffs are Silverbrook, EP 0771 658 A2 actuator does not move. required to eliminate moving and related patent applications parts Tone-jet

NOZZLE REFILL METHOD Description Advantages Disadvantages Examples Surface tension This is the normal way that in Fabrication simplicity Low speed Thermal ink jet jets are refilled. After the Operational simplicity Surface tension force relatively Piezoelectric ink jet actuator is energized, it typically small compared to actuator force IJ01-IJ07, IJ10-IJ14, IJ16, IJ20, returns rapidly to its normal Long refill time usually IJ22-IJ45 position. This rapid return sucks dominates the total repetition in air through the nozzle open- rate ing. The ink surface tension at the nozzle then exerts a small force restoring the meniscus to a minimum area. This force refills the nozzle. Shuttered Ink to the nozzle chamber is High speed Requires common ink pressure IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, oscillating provided at a pressure that Low actuator energy, as the oscillator IJ21 ink pressure oscillatees at twice the drop actuator need only open or close May not be suitable for ejection frequency. When a the shutter, instead of ejecting pigmented inks drop is to be ejected, the the ink drop shutter is opened for 3 half cycles: drop ejection, actuator return, and refill. The shutter is then closed to prevent the nozzle chamber emptying during the next negative pressure cycle. Refill actuator After the main actuator has High speed, as the nozzle is Requires two independent IJ09 ejected a drop a second (refill) actively refilled actuators per nozzle actuator is energized. The refill actuator pushes ink into the nozzle chamber. The refill actuator returns slowly, to prevent its return from emptying the chamber again. Positive ink The ink is held a slight positive High refill rate, therefore a Surface spill must be prevented Silverbrook, EP 0771 658 A2 pressure pressure. After the ink drop is high drop repetition rate is Highly hydrophobic print head and related patent applications ejected, the nozzle chamber fills possible surfaces are required Alternative for: IJ01-IJ07, IJ10- quickly as surface tension and IJ14, IJ16, IJ20, IJ22-IJ45 ink pressure both operate to refill the nozzle.

METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Description Advantages Disadvantages Examples Long inlet The ink inlet channel to the Design simplicity Restricts refill rate Thermal ink jet channel nozzle chamber is made long Operational simplicity May result in a relatively large Piezoelectric ink jet and relatively narrow, relying Reduces crosstalk chip area IJ42, IJ43 on viscous drag to reduce inlet Only partially effective back-flow. Positive ink The ink is under a positive Drop selection and separation Requires a method (such as a Silverbrook, EP 0771 658 A2 pressure pressure, so that in the quiescent forces can be reduced nozzle rim or effective hydro- and related patent applications state some of the ink drop Fast refill time phobizing, or both) to prevent Possible operation of the follow- already protrudes from the flooding of the ejection surface ing: IJ01-IJ07, IJ09-IJ12, nozzle. This reduces the pressure of the print head. IJ14, IJ16, IJ20, IJ22, IJ23-IJ34, in the nozzle chamber which is IJ36-IJ41, IJ44 required to eject a certain volume of ink. The reduction in chamber pressure results in a reduction in ink pushed out through the inlet. Baffle One or more baffles are placed The refill rate is not as restricted Design complexity HP Thermal Ink Jet in the inlet ink flow. When the as the long inlet method. May increase fabrication Tektronix piezoelectric ink jet actuator is energized, the rapid Reduces crosstalk complexity (e.g. Tektronix hot ink movement creates eddies melt Piezoelectric print heads). which restrict the flow through the inlet. The slower refill process is unrestricted, and does not result in eddies. Flexible flap In this method recently disclosed Significantly reduces back-glow Not applicable to most ink jet Canon restricts inlet by Canon, the expanding for edge-shooter thermal ink jet configurations actuator (bubble) pushes on a devices Increased fabrication complexity flexible flap that restricts the Inelastic deformation of polymer inlet. flap results in creep over extended use Inlet filter A filter is located between the Additional advantage of ink Restricts refill rate IJ04, IJ12, IJ24, IJ27, IJ29, IJ30 ink inlet and the nozzle filtration May result in complex chamber. The filter has a Ink filter may be fabricated construction multitude of small holes or slots, with no additional process steps restricting ink flow. The filter also removes particles which may block the nozzle. Small inlet The ink inlet channel to the Design simplicity Restricts refill rate IJ02, IJ37, IJ44 compared to nozzle chamber has a May result in a relatively large nozzle substantially smaller cross chip area section than that of the Only partially effective nozzle, resulting in easier ink egress out of the nozzle than out of the inlet. Inlet shutter A secondary actuator controls Increases speed of the ink-jet Requires separate refill actuator IJ09 the position of a shutter, closing print head operation and drive circuit off the ink inlet when the main actuator is energized. The inlet is The method avoids the problem Back-flow problem is eliminated Requires careful design to IJ01, IJ03, IJ05, IJ06, IJ07, IJ10, located behind of inlet back-flow by arranging minimize the negative pressure IJ11, IJ14, IJ16, IJ22, IJ23, IJ25, the ink-pushing the ink-pushing surface of the behind the paddle IJ28, IJ31, IJ32, IJ33, IJ34, IJ35, surface actuator between the inlet and IJ36, IJ39, IJ40, IJ41 the nozzle. Part of the The actuator and a wall of the Significant reductions in back- Small increase in fabrication IJ07, IJ20, IJ26, IJ38 actuator moves ink chamber are arranged so that flow can be achieved complexity to shut off the the motion of the actuator closes Compact designs possible inlet off the inlet. Nozzle actuator In some configurations of ink Ink back-flow problem is None related to ink back-flow on Silverbrook, EP 0771 658 A2 does not result jet, there is no expansion or eliminated actuation and related patent applications in ink back- movement of an actuator which Valve-jet flow may cause ink back-flow Tone-jet through the inlet.

NOZZLE CLEARING METHOD Description Advantages Disadvantages Examples Normal nozzle All of the nozzles are fired No added complexity on the May not be sufficient to displace Most ink jet systems firing periodically, before the ink has a print head dried ink IJ01, IJ02, IJ03, IJ04, IJ05, IJ06, chance to dry. When not in use IJ07, IJ09, IJ10, IJ11, IJ12, IJ14, the nozzles are sealed (capped) IJ16, IJ20, IJ22, IJ23, IJ24, IJ25, against air. The nozzle firing is IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, usually performed during a IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, special clearing cycle, after IJ39, IJ40, IJ41, IJ42, IJ43, IJ44, first moving the print head to a IJ45 cleaning station. Extra power In systems which heat the ink, Can be highly effective if the Requires higher drive voltage for Silverbrook, EP 0771 658 A2 to ink heater but do not boil it under normal heater is adjacent to the nozzle clearing and related patent applications situations, nozzle clearing can May require larger drive be achieved by over-powering transistors the heater and boiling ink at the nozzle. Rapid The actuator is fired in rapid Does not require extra drive Effectiveness depends May be used with: IJ01, IJ02, succession of succession. In some configura- circuits on the print head substantially upon the IJ03, IJ04, IJ05, IJ06, IJ07, IJ09, actuator pulses tions, this may cause heat build- Can be readily controlled and configuration of the ink jet IJ10, IJ11, IJ14, IJ16, IJ20, IJ22, up at the nozzle which boils the initiated by digital logic nozzle IJ23, IJ24, IJ25, IJ27, IJ28, IJ29, ink, clearing the nozzle. In other IJ30, IJ31, IJ32, IJ33, IJ34, IJ36, situations, it may cause IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, sufficient vibrations to dislodge IJ43, IJ44, IJ45 clogged nozzles. Extra power to Where an actuator is not A simple solution where Not suitable where there is a May be used with: IJ03, IJ09, ink pushing normally driven to the limit of applicable hard limit to actuator movement IJ16, IJ20, IJ23, IJ24, IJ25, IJ27, actuator its motion, nozzle clearing may IJ29, IJ30, IJ31, IJ32, IJ39, IJ40, be assisted by providing an IJ41, IJ42, IJ43, IJ44, IJ45 enhanced drive signal to the actuator. Acoustic An ultrasonic wave is applied to A high nozzle clearing capability High implementation cost if IJ08, IJ13, IJ15, IJ17, IJ18, IJ19, resonance the ink chamber. This wave is of can be achieved system does not already include IJ21 an appropriate amplitude and May be implemented at very low an acoustic actuator frequency to cause sufficient cost in systems which already force at the nozzle to clear include acoustic actuators blockages. This is easiest to achieve if the ultrasonic wave is at a resonant frequency of the ink cavity. Nozzle clearing A microfabricated plate is Can clear severely clogged Accurate mechanical alignment Silverbrook, EP 0771 658 A2 plate pushed against the nozzles. The nozzles is required and related patent applications plate has a post for every Moving parts are required nozzle. A post moves through There is risk of damage to the each nozzle, displacing dried nozzles ink. Accurate fabrication is required Ink pressure The pressure of the ink is May be effective where other Requires pressure pump or other May be used with all IJ series pulse temporarily increased so that ink methods cannot be used pressure actuator ink jets streams from all of the nozzles. Expensive This may be used in conjunction Wasteful of ink with actuator energizing. Print head A flexible ‘blade’ is wiped Effective for planar print head Difficult to use if print head Many ink jet systems wiper across the print head surface. surfaces surface is non-planar or very The blade is usually fabricated Low cost fragile from a flexible polymer, e.g. Requires mechanical parts rubber or synthetic elastomer. Blade can wear out in high volume print systems Separate ink A separate heater is provided at Can be effective where other Fabrication complexity Can be used with many IJ series boiling heater the nozzle although the normal nozzle clearing methods cannot ink jets drop e-ection mechanism does be used not require it. The heaters do Can be implemented at no not require individual drive additional cost in some ink jet circuits, as many nozzles can be configurations cleared simultaneously, and no imagining is required.

NOZZLE PLATE CONSTRUCTION Description Advantages Disadvantages Examples Electroformed A nozzle plate is separately Fabrication simplicity High temperatures and pressures Hewlett Packard Thermal Ink jet nickel fabricated from electroformed are required to bond nozzle plate nickel, and bonded to the print Minimum thickness constraints head chip. Differential thermal expansion Laser ablated Individual nozzle holes are No masks required Each hole must be individually Canon Bubblejet or drilled ablated by an intense UV laser Can be quite fast formed 1988 Sercel et al., SPIE, Vol. polymer in a nozzle plate, which is Some control over nozzle profile Special equipment required 998 Excimer Beam Applica- typically a polymer such as is possible Slow where there are many tions, pp. 76-83 polyimide or polysulphone Equipment required is relatively thousands of nozzles per print 1993 Watanabe et al., U.S. Pat. low cost head No. 5,208,604 May produce thin burrs at exit holes Silicon micro- A separate nozzle plate is micro- High accuracy is attainable Two part construction K. Bean, IEEE Transactions on machined machined from single crystal High cost Electron Devices, Vol. ED-25, silicon, and bonded to the print Requires precision alignment No. 10, 1978, pp 1185-1195 head wafer. Nozzles may be clogged by Xerox 1990 Hawkins et al., U.S. adhesive Pat. No. 4,899,181 Glass Fine glass capillaries are drawn No expensive equipment Very small nozzle sizes are 1970 Zoltan U.S. Pat. No. capillaries from glass tubing. This method required difficult to form 3,683,212 has been used for making Simple to make single nozzles Not suited for mass production individual nozzles, but is difficult to use for bulk manufacturing of print heads with thousands of nozzles. Monolithic, The nozzle plate is deposited as High accuracy (<1 μm) Requires sacrificial layer under Silverbrook, EP 0771 658 A2 surface micro- a layer using standard VLSI Monolithic the nozzle plate to form the and related patent applications machined using deposition techniques. Nozzles Low cost nozzle chamber IJ01, IJ02, IJ04, IJ11, IJ12, IJ17, VLSI litho- are etched in the nozzle plate Existing processes can be used Surface may be fragile to the IJ18, IJ20, IJ22, IJ24, IJ27, IJ28, graphic using VLSI lithography and touch IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, processes etching. IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Monolithic, The nozzle plate is a buried High accuracy (<1 μm) Requires long etch times IJ03, IJ05, IJ06, IJ07, IJ08, IJ09, etched through etch stop in the wafer. Nozzle Monolithic Requires a support wafer IJ10, IJ13, IJ14, IJ15, IJ16, IJ19, substrate chambers are etched in the front Low cost IJ21, IJ23, IJ25, IJ26 of the wafer, and the wafer is No differential expansion thinned from the back side. Nozzles are then etched in the etch stop layer. No nozzle plate Various methods have been tried No nozzles to become clogged Difficult to control drop Ricoh 1995 Sekiya et al U.S. to eliminate the nozzles entirely, position accurately Pat. No. 5,412,413 to prevent nozzle clogging. Crosstalk problems 1993 Hadimioglu et al EUP These include thermal bubble 572,220 mechanisms and acoustic lens mechanisms Trough Each drop ejector has a trough Reduced manufacturing Drop firing direction is sensitive IJ35 through which a paddle moves. complexity to wicking. There is no nozzle plate. Monolithic Nozzle slit The elimination of nozzle holes No nozzles to become clogged Difficult to control drop 1989 Saito et al U.S. Pat. No. instead of and replacement by a slit position accurately 4,799,068 individual encompassing many actuator Crosstalk problems nozzles positions reduces nozzle clogging, but increases cross- talk due to ink surface waves

DROP EJECTION DIRECTION Description Advantages Disadvantages Examples Edge (‘edge Ink flow is along the surface of Simple construction Nozzles limited to edge Canon Bubblejet 1979 Endo shooter’) the chip, and ink drops are No silicon etching required High resolution is difficult et al GB patent 2,007,162 ejected from the chip edge. Good head sinking via substrate Fast color printing requires one Xerox heater-in-pit 1990 Mechanically strong print head per color Hawkins et al U.S. Pat. No. Ease of chip handing 4,899,181 Tone-jet Surface (‘roof Ink flow is along the surface of No bulk silicon etching required Maximum ink flow is severely Hewlett-Packard TIJ 1982 shooter’) the chip, and ink drops are Silicon can make an effective restricted Vaught et al U.S. Pat. No. ejected from the chip surface, heat sink 4,490,728 normal to the plane of the chip. Mechanical strength IJ02, IJ11, IJ12, IJ20, IJ22 Through chip, Ink flow is through the chip, and High ink flow Requires bulk silicon etching Silverbrook, EP 0771 658 A2 forward (‘up ink drops are ejected from the Suitable for pagewidth print and related patent applications shooter’) front surface of the chip. heads IJ04, IJ17, IJ18, IJ24, IJ27-IJ45 High nozzle packing density therefore low manufacturing cost Through chip, Ink flow is through the chip, High ink flow Requires wafer thinning IJ01, IJ03, IJ05, IJ06, IJ07, IJ08, reverse (‘down and ink drops are ejected from Suitable for pagewidth print Requires special handling during IJ09, IJ10, IJ13, IJ14, IJ15, IJ16, shooter’) the rear surface of the chip. heads manufacture IJ19, IJ21, IJ23, IJ25, IJ26 High nozzle packing density therefore low manufacturing cost Through Ink flow is through the actuator, Suitable for piezoelectric print Pagewidth print heads require Epson Stylus actuator which is not fabricated as part of heads several thousand connections to Tektronix hot melt piezoelectric the same substrate as the drive drive circuits ink jets transistors. Cannot be manufactured in standard CMOS fabs Complex assembly required

INK TYPE Description Advantages Disadvantages Examples Aqueous, dye Water based ink which typically Environmentally friendly Slow drying Most existing ink jets contains: water, dye, surfactant, No odor Corrosive All IJ series ink jets humectant, and biocide. Modern Bleeds on paper Silverbrook, EP 0771 658 A2 ink dyes have high water- May strikethrough and related patent applications fastness, light fastness Cockles paper Aqueous, Water based ink which typically Environmentally friendly Slow drying IJ02, IJ04, IJ21, IJ26, IJ27, IJ30 pigment contains: water, pigment, No odor Corrosive Silverbrook, EP 0771 658 A2 surfactant, humectant, and Reduced bleed Pigment may clog nozzles and related patent applications biocide. Reduced wicking Pigment may clog actuator Piezoelectric ink-jets Reduced strikethrough mechanisms Thermal ink jets (with signifi- Cockles paper cant restrictions) Methyl Ethyl MEK is a highly volatile solvent Very fast drying Odorous All IJ series ink jets Ketone (MEK) used for industrial printing on Prints on various substrates such Flammable difficult surfaces such as as metals and plastics aluminum cans. Alcohol Alcohol based inks can be used Fast drying Slight odor All IJ series ink jets (ethanol, where the printer must operate at Operates at sub-freezing Flammable 2-butanol, and temperatures below the freezing temperatures others) point of water. An example of Reduced paper cockle this is in-camera consumer Low cost photographic printing. Phase change The ink is solid at room No drying time-ink instantly High viscosity Tektronix hot melt piezoelectric (hot melt) temperature, and is melted in the freezes on the print medium Printed ink typically has a ink jets print head before jetting. Hot Almost any print medium can be ‘waxy’ feel 1989 Nowak U.S. Pat. No. melt inks are usually wax based, used Printed pages may ‘block’ 4,820,346 with a melting point around No paper cockle occurs Ink temperature may be above All IJ series ink jets 80° C.. After jetting the ink No wicking occurs the curie point of permanent freezes almost instantly upon No bleed occurs magnets contacting the print medium or No strikethrough occurs Ink heaters consume power a transfer roller. Long warm-up time Oil Oil based inks are extensively High solubility medium for High viscosity: this is a All IJ series ink jets used in offset printing. They some dyes significant limitation for use in have advantages in improved Does not cockle paper ink jets, which usually require a characteristics on paper Does not wick through paper low viscosity. Some short chain (especially no wicking or and multi-branched oils have a cockle). Oil soluble dies and sufficiently low viscosity. pigments are required. Slow drying Microemulsion A microemulsion is a stable, self Stop ink bleed Viscosity higher than water All IJ series ink jets forming emulsion of oil, water, High dye solubility Cost is slightly higher than and surfactant. The characteristic Water, oil, and amphiphilic water based ink drop size is less than 100 nm, soluble dies can be used High surfactant concentration and is determined by the Can stabilize pigment required (around 5%) preferred curvature of the suspensions surfactant. 

What is claimed is:
 1. A micro electro-mechanical nozzle arrangement which comprises nozzle chamber walls defining a nozzle chamber and a moveable actuator positioned within the nozzle chamber, so that, upon actuation of the actuator, a water-based liquid within the nozzle chamber is displaced from the nozzle chamber, the actuator having a first surface which applies an actuating force on the liquid and a second, opposed: surface, wherein the second surface is of a hydrophobic material so that the liquid is repelled from a region about the second surface, thereby facilitating movement of the actuator.
 2. A micro electro-mechanical nozzle arrangement as claimed in claim 1, in which portions of the nozzle chamber walls about the second surface of the actuator are of a hydrophobic material.
 3. A method of facilitating operation of a micro electro-mechanical nozzle arrangement which comprises nozzle chamber walls defining a nozzle chamber and a moveable actuator positioned within the nozzle chamber so that, upon actuation of the actuator, a water-based liquid within the nozzle chamber is displaced from the nozzle chamber, the actuator having a first surface which applies an actuating force on the liquid and a second, opposed surface, the method including the step of: imparting hydrophobic properties to the second surface, so that the liquid is repelled from the second surface.
 4. The method as claimed in claim 3, which includes the step of imparting hydrophobic properties to portions of the nozzle chamber walls about the second surface of the actuator. 